The present invention concerns the shotgun, shooting, military etc., sector in general and refers in particular to a butt pad for these firearms.
Firearms usually have a wooden stock with a so-called butt pad fitted to the bottom as protection against the stock cracking when the firearm is stood up or to rest against the shoulder of the shooter when the firearm is being used. Butt pads are usually made out of a single homogenous material, generally rubbery, comparatively elastic and soft, honeycombed or non-honeycombed, to fit the shoulder of the shooter and to soften the blow from the recoil received from the firearm following firing.
In a firearm free to recoil, in order to reach the desired muzzle velocity, the acceleration of the propelling charge is always generated at the expense of an acceleration in the opposite direction of the firearm itself or recoil xe2x80x9cmassxe2x80x9d.
In particular, in an individual firearm, such as a rifled or smoothbore shotgun assumed free to retract, the quantity of motion M*V conventionally acquired by said firearm at the moment the charge exits the muzzle of the barrel, Is equal in value and opposite in sign compared to the quantity of motion m*v of the load, where the symbols M, V, m, v, indicate respectively the mass and the velocity of the firearm and the load. A corresponding amount of Kinetic energy is associated with the recoil velocity of the firearm, energy where the shoulder of the shooter the stock and relative butt pad of the firearm usually rests against, will be called on to contrast and annul by undertaking an action of resistance.
This work and consequently the force the shoulder exerts in order to slow down and then stop the retrograde motion of the firearm will, due to the considerations given above regarding the quantity of motion, be greater in proportion to the value of the mass and the velocity of the propelling charge and less in proportion to the mass of the firearm.
Techniques today enable arms to be manufactured that tend to be lighter but nevertheless reliable and at the same time there has been a progressive increase, for example in shotgun cartridges available on the market, in the quantity of the mass of the maximum propelling load. All this has made the problem of the xe2x80x9crecoilxe2x80x9d action of a shotgun against the shoulder more serious.
In the attempt to decrease the force against the shoulder and the consequent inconvenience suffered by the shooter, various solutions have been devised over the years as regards to butt pads for shotguns and/or sporting guns.
For example, in the so-called xe2x80x9choneycombedxe2x80x9d type of rubber butt pads, attempts have been made to optimise the structure of the butt pad so as to make it xe2x80x9cselectivelyxe2x80x9d more pliable according to the axis of the firearm, maintaining at the same time good lateral stability. This effect is achieved by carefully studying the position and shape of the xe2x80x9cemptyxe2x80x9d and xe2x80x9csolidxe2x80x9d sections of the butt pad itself.
These types of butt pad, although having the advantage of being more pliable and therefore having a longer xe2x80x9cstrokexe2x80x9d in opposition to the motion of the firearm, have, because of this, an increased relative motion between the stock and the face of the shooter in that he rests his cheek on it and this can be troublesome or even cause microtraumas.
Furthermore these types of butt pads, because of the way in which they are constructed, which implies irremovable and unacceptable moulding faults on the side surfaces of the same, must be fitted to the profile of the stock on which it is assembled with consequent increase in costs and loss of possibility to interchange.
In other types of butt pad, other soft materials with particular characteristics favouring absorption were used. Even in this case, however, the inconvenience of having to support xe2x80x9crubbingxe2x80x9d of the stock against the cheek remains. In general these materials, having modest mechanical resistance characteristics, are easily damaged and suffer from wear that shortens their lifespan. There are examples where the dissipation of recoil energy is achieved by shock absorbers (operating hydraulically, with springs, with elastomers, by friction) inserted in the stock and connected to the butt pad using an actuator head. In this way, the desired effect is achieved through a force counteracting the recoil motion and the relative passive dissipation associated with the relative motion between stock and butt pad.
These butt pads, although usually characterised by good efficiency, do however, as can easily be imagined, present manufacturing complications of a mechanical nature, and are also more expensive.
Given the above the aim of the present invention is to supply a butt pad having a new conception so as to reduce the discomfort deriving from recoil following firing of an individual firearm held against the shoulder.
Another aim of the invention is to submit a specific method of fixing the butt pad to the stock, so as to take full advantage of the characteristics of the new butt pad.
From observing the technical components in the field of sporting goods, the use of materials having particular properties so as to protect the bone and muscle structure involved in the sporting activity in question, is well known.
Usually these materials are characterised by high energy absorption achieved by internal dissipation (viscous effect) and are used in combination with other materials, generally having a retaining function, in order to lessen the repeated impulsive stress deriving from the sport practised, otherwise often responsible for known pathologies.
This is the case, for example, of the soles of shoes for jogging where, inside the sole itself which acts as a retainer, there is a gel cushion, or bicycle saddles where, in the same way, this material is placed inside the saddle in line with the perineal zone.
The function of these materials is to deform, due to external actions, so that:
Part of the energy due to the impulsive stress (or impact) is absorbed; this energy will then be dissipated by the material due to its internal resistance (viscosity);
The impact stress is spread as uniformly as possible over the anatomic part in question (for example the arch of the foot, the shoulder); this effect is achieved, during the shock absorbing action, by hydrostatic distribution of the pressure inside the housing.
The abovementioned aims of the invention are achieved, in line with the concepts based on some of the technical components already mentioned, in a composite structured butt pad which includes an elastically variable shaped external sheath, a high viscosity element housed in said sheath and congruent with the variations in shape of the latter, and a base element and semi-rigid support attached to the sheath and designed for fitting the butt pad to the stock of a firearm.